Solvent-dependent intra- and intermolecular vibrational energy transfer from the triply degenerate CO stretch mode Of W(CO)(6) is observed in nine alkanes (CnH2n+2, n = 5-13) with single-color sub-picosecond time-resolved infrared spectroscopy. In all the solvents, the vibrational relaxation process is well characterized by three time constants: tau(1) (< 1 PS), tau(2) (3-13 ps) and tau(3) (124-160 ps). The solvent dependence of tau(2) and tau(3) cannot be explained by the macroscopic properties of the solvent. In particular, the longest time constant tau(3) shows the minimum value of 124 ps in decane among the nine alkanes. The rate of the vibrational energy relaxation is a sensitive measure of the microscopic environments. (c) 2005 Elsevier B.V. All rights reserved.